337 TODO

   337 So far, every obsolete changeset we have seen is also hidden. However,

   338 these are *not* the same thing—that's why they have different names.

   339 It's entirely possible to have obsolete changesets that are not

   340 hidden. We'll see examples of that soon, when we create *unstable*

   341 changesets.

   342 

   343 Note that all hidden changesets are obsolete: hidden is a subset of

   344 obsolete.